Adhering and Developing the Gelatin Tissue
In preparing an intaglio plate for etching, a resist is used to control the etch and create an image. In photogravure this resist is made from the photographic contour map of gelatin. The exposed gelatin tissue is immediately adhered to a copper plate, then developed in hot water. Hot water is used for the wash-out development process to effectively remove all of the unexposed or underexposed gelatin and leave the tanned gelatin image intact on the surface of the plate. This three-dimensionally contoured rendition of the original image will act as a graduated acid resist for the copper plate. The extremely narrow range of thickness within this resist layer is from virtually nil in the darkest blacks to about 15 microns (0.015 mm) in the densest highlights (Crawford 1979, pp. 103-104). Control of this process depends on stable temperatures and clean solutions.